Apparatus for the production of electric oscillations



p 1940- A. H. s. WALKER ET AL 5,893

APPARATUS FOR THE PRODUCTION OF ELECTRIC OSCILLATIONS Filed Dec. 21, 1939 Tram ATTORNEY Patented Sept. 24, 1940 UNITED STATES APPARATUS FOR THE PRODUCTION OF ELECTRIC OSCILLATIONS Alec Hervey Bennett Walker and Edward Alfred Sheppard, London, England,

assignors, by

mesne assignments, to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application December 21, 1939, Serial No. 310,428 In Great Britain December 23, 1938 2 Claims.

This invention relates to apparatus for the production of electric: oscillations and has for its object to provide improved apparatus of this character adapted to be operated from an alternating current supply circuit and to produce oscillations of a frequency which may be arranged to have any desired value lower than the supply frequency.

According to the invention, the apparatus comlC' prises an oscillation circuit containing inductance and capacity connected to the alternating current circuit, the inductance comprising a magnetic core having such flux saturation characteristics that the combined capacity and inductance has a rising current-voltage or negative resistance characteristic over at least a portion of its regulation curve, the oscillation circuit also including an ohmic resistance having a positive temperature coefiicient, the current-voltage characteristic of 2c the ohmic resistance being so related to that of the combined capacity and inductance that the current in the oscillation circuit will vary periodically as the resistance alternately heats and cools.

2:5 This periodic variation is of course, superposed as a modulation upon the current alternation at the supply circuit frequency, but by connecting the ohmic resistance to the oscillation circuit through a suitable rectifier so that the input ter- 3 minals of the rectifier are connected in series in the oscillation circuit while its output terminals are connected to a load circuit including the ohmic resistance, a simple unmodulated oscillating current will be produced in the delivery cir- 35 cuit which is lower than but otherwise independent of the supply circuit frequency.

In carrying the invention into practice, the ohmic resistance is preferably constituted by a gas-filled metal filament incandescent lamp of suitable resistance and temperature coefficient, the frequency of the oscillation current produced being determined by the rate of heating and cooling of the lamp filament while the amplitude of the oscillation is dependent upon the current- 45 voltage characteristics of the combined capacity and inductance and of the lamp filament.

The oscillation circuit includes a suitable condenser and saturated inductance connected in series with one another and in series either di- 50 rectly or through a transformer or rectifier with the metal filament lamp, the oscillation circuit being connected to the alternating current supply circuit either directly or through a suitable transformer.

5 In operation, the initial fiow of current in the oscillation circuit when the latter is connected to the supply circuit, corresponds in magnitude to the cold resistance of the lamp filament and as this filament becomes heated, the current is reduced to a value determined by the current- 5 voltage characteristics above referred to, whereupon the lamp filament cools, this cycle being repeated continuously.

In order that the present invention may be readily understood, it will now be described by way of example with reference to the accompanying drawing of which:

Figure 1 is a circuit diagram, illustrating an embodiment of the invention, while Figures 2 and 3 are voltage-current diagrams.

Referring now first to Figure 1, it will be seen that the terminals Br and S of an alternatingcurrent supply circuit are shown as connected to an oscillation circuit which comprises a condenser C connected in series with an inductance L having an iron core of suitable saturation characteristics and an incandescent lamp K constituting an ohmic resistance having a positive tem perature characteristic. A load circuit may be connected to the terminals X and Y thus being connected in parallel with the lamp K, or may be connected in series with. the elements of the 0scillation circuit. As illustrated, the input terminals of a rectifier system I) are connected in series in the oscillation circuit, the ouput ter- 39 minals of the rectifier system D being connected to the terminals X and Y of a suitable load such as an impedance B.

In the diagram of Figure 2, the voltages developed at the terminals of the inductance L and of the condenser C are shown as functions or" the magnitude of the current. It will be observed that, while (the frequency of the current supplied being constant) the voltage across the condenser C is represented by the straight line 40 through the origin 0, the curve for the voltage across the inductance coil L comprises a relatively steep initial portion corresponding to the nonsaturated condition of the iron core, and continues as a substantially flatter portion corresponding to the increasing saturation condition of the iron core. Assuming that the influence of the external load is negligible, the voltage across the resistance K corresponds to the vector 50 difference between the voltage of the alternatingcurrent supply circuit and the vector sum of the voltages across the condenser C and across the inductance coil L, the value of this sum being substantially equal to the difierence of the volt- 5 ages involved since the phases of the two voltages are substantially 180 degrees apart.

In the diagram of Figure 3, the voltage across the ohmic resistance K is shown by the curved line as afunction of the current, while the straight lines H, C, and C indicate the voltage-current characteristics of the ohmic resistance K corresponding to difierent temperatures. Since, of course, the resistance drop of voltage across the resistance K must at any time be equal to the voltage applied thereto, the actual current flowing at a given temperature is determined by the intersection of the ciuved line with the straight line corresponding to this temperature.

When current is first supplied to the circuit, the ohmic resistance being at substantially room temperature, its characteristic corresponds to the line C and a relatively large current Ic will therefore flow in the circuit and will rapidly heat the resistance element K, the current gradually decreasing in accordance with the increasing temperature, until a current value la is attained for which the characteristic H of the ohmic resistance element forms a tangent to the curved characteristic for the applied voltage. This, as is well known, corresponds to an instable condition under which the current suddenly decreases to the value IH which corresponds to a second point of intersection of the curved line with the line H corresponding to a stable condition. Under these conditions, however, the current flowing through the resistance element K is insuiiicient to maintain this element at the high temperature previously attained, and the temperature of the resistance element K will accordingly fall, this fall being accompanied by a gradual increase in the current from the value In to the value In, until the characteristic of the resistance element corresponds to the line C, at which an instable condition again occurs, the current rising suddenly from the value In to the much higher value Io, which is again sufficient rapidly to raise the temperature of the resistance element K. It will thus be evident that the temperature of the resistance element K will be periodically raised from a value corresponding to the line C to a value corresponding to the line H and will fall again to the former value, the current oscillating correspondingly between the values Io and In.

This action may evidently be utilised for producing periodical variations in the light emitted from the incandescent lamp K, but the periodically varying current may also be utilised in an external load circuit. In the latter case, as will be evident, the lines H, C, and C" will be replaced by curves or lines corresponding to the total drop of voltage across the load and the resistance element K.

If a load is simply connected across the terminals X and Y or connected in series with the elements C and L, the load will be supplied with current of the frequency of the supply circuit modulated in accordance with the periodically varying resistance of the element K, but a substantially unmodulated current supply having a frequency determined by the action of the element K can be obtained by the provision of a rectifier system D as shown in Figure 1, the input terminals of the rectifier system D being connected in the oscillation circuit in series with the condenser C and the inductance L, the load B being connected to the output terminals of the rectifier system D, and the current derived from the terminals X and Y may similarly be converted into unmodulated oscillating current by the provision of a suitable rectifier arrangement as will be readily understood.

The invention is evidently not limited to the particular arrangement and connection of the various electrical elements utilised as above illustrated and described by way of example.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

1. Apparatus for the production of electric oscillations, comprising an oscillation circuit containing inductance and capacity connected to the alternating current supply circuit, the inductance comprising a magnetic core having such flux saturation characteristics that the combined capacity and inductance has a rising current-voltage or negative resistance characteristic over at least a portion of its regulation curve, the oscillation circuit also including an ohmic resistance having a positive temperature coefficient, the currentvoltage characteristic of the ohmic resistance being so related to that of the combined capacity and inductance that the current in the oscillation circuit will vary periodically as the resistance alternately heats and cools.

2. Apparatus as claimed in claim 1, in which the ohmic resistance is connected to the oscillation circuit through a suitable rectifier so that the input terminals of the rectifier are connected in series in the oscillation circuit while its output terminals are connected to a load circuit, for the purpose specified.

ALEC HERVEY BENNETT WALKER. EDWARD ALFRED SHEPPARD. 

